1. Field:
The present disclosure relates generally to optical communications and, in particular, to transmitting information. Still more particularly, the present disclosure relates to a method and apparatus for transmitting information from multiple optical sources.
2. Background:
When transmitting information, different environments may be better suited than other environments for use of different components in a communications system. For example, with optical communications, a transmitter for optical signals may perform better in one type of environment than a receiver of the optical signal. As a result, in some environments, the transmitter may be able to transmit optical signals with a desired quality over greater distances. However, the receiver may be unable to detect the optical signal as well as desired in that particular environment.
For example, other optical signals may be present in the environment other than the optical signal transmitted from the transmitter to the receiver. These optical signals may be the result of sources other than from the transmitter of the optical signal meant to be detected by the receiver. These other optical signals may be background signals from various sources in the environment. These various sources of optical signals may be, for example, without limitation, reflections of sunlight, other optical signal transmitters, light sources and other sources that may reflect or transmit background signals in the environment. In these illustrative examples, light sources may include, for example, lights on buildings or vehicles. Reflections of sunlight may occur on buildings or vehicles.
The receiver may have difficulty detecting the transmitted optical signal with other optical signals being present in the environment. These other optical signals may have one or more characteristics that are similar to the optical signal that is to be detected. For example, these other optical signals may have similar frequencies, polarizations, and other characteristics that are similar to the optical signal that is to be detected. Thus, detection of the desired optical signal may be more difficult than desired.
In optical communications, considerable effort has been made to develop receivers that are able to identify an optical signal transmitted at a particular frequency from other optical signals that may be present in the environment. Techniques, such as single frequency filtering, have been employed. These techniques use frequency spatial timing polarization to select the correct transmission frequency for a communications link.
For example, single frequency filtering employs filters that separate the input signal into multiple components. As a result of the single frequency filtering, each component carries a single frequency sub-band of the original signal.
Depending on the environment, identifying the signal may be more challenging than desired even with currently used techniques for identifying optical signals. Therefore, it would be desirable to have a method and apparatus that takes into account at least some of the issues discussed above, as well as other possible issues.